Method of producing a device with transistors strained by means of an external layer
A method of producing a microelectronic device with transistors wherein a strain layer is formed on a series of transistors and the strain exerted on at least one given transistor of said series is released by removing a sacrificial layer situated between said given transistor and said strain layer.
1. A method of producing a microelectronic device with transistors comprising the steps of:
a) forming a strain layer on a first gate block of a transistor of a first type and on first semi-conductor areas situated on either side of said first gate block, as well as on a second gate block of a transistor of a second type and on second semi-conductor areas situated on either side of said second gate block, a sacrificial layer being provided between said strain layer and said second semi-conductor areas of the transistor of the second type,
b) forming openings traversing the strain layer among which one or more given openings exposing the sacrificial layer,
c) removing the sacrificial layer by etching through said openings.
2. The method according to claim 1 , wherein among the openings formed at step b) one or more openings revealing the first semi-conductor areas.
3. The method according to claim 2 , the method moreover comprising, after step c), the deposition of a metallic material through said openings, followed by an annealing, so as to form areas of alloy of metal and semi-conductor.
4. The method according to claim 3 , wherein the type of metallic material deposited, the volume of metallic material deposited on the first semi-conductor areas, as well as the duration of the annealing are chosen so as to form first areas of alloy of metal and semi-conductor exerting a compressive strain on a channel area of said transistor of the first type.
5. The method according to claim 3 , wherein the removal of the sacrificial layer by etching through said given openings leads to the formation of cavities between said second semi-conductor areas and said strain layer, said metallic deposition and said annealing being carried out so as to form second areas of alloy of metal and semi-conductor partially filling said cavities, a space being conserved between said second areas of alloy of metal and semi-conductor and said strain layer.
6. The method according to claim 1 , wherein the first gate block and the second gate block rest on a semi-conductor layer, the first semi-conductor areas and/or the second semi-conductor areas being formed by growth on said semi-conductor layer.
7. The method according to claim 6 , the method moreover comprising, prior to said growth: a thinning of said semi-conductor layer in areas situated on either side of said first gate block and/or of said second gate block.
8. The method according to claim 6 , the first semi-conductor areas being formed of a semi-conductor material provided to compressive strain said semi-conductor layer on which said first gate block rests.
9. The method according to claim 6 , the second semi-conductor areas being formed of a semi-conductor material provided to tensile strain said semi-conductor layer on which said second gate block rests.
10. The method according to claim 1 , wherein prior to step a), insulating spacers are formed against said first gate block and said second gate block, said strain layer resting on said spacers.
11. The method according to claim 1 , wherein the strain layer is separated from said second semi-conductor areas by an etching stop layer, the removal at step c) of the sacrificial layer by etching through said given openings being carried out until reaching said etching stop layer.
12. The method according to claim 1 , wherein the strain layer is based on a dielectric material such as silicon nitride.
13. The method according to claim 1 , moreover comprising between step a) and step b), the steps of:
depositing at least one insulating layer on the strain layer,
forming holes traversing said insulating layer and exposing said strain layer by selective etching of said insulating layer vis-à-vis said strain layer.
14. The method according to claim 1 , wherein the first gate block and/or said second gate block are based on at least one sacrificial material, the method moreover comprising, after step c), the steps of:
removing the strain layer on said first gate block and/or on said second gate block so as to expose said sacrificial material,
removing said sacrificial material,
replacing said sacrificial material by at least one other gate material.